Primary cell with plural u-shaped magnesium anode assemblies



June 25, 1968 c. E. NELSON 3,390,016

PRIMARY CELL WITH PLURAL U-SHAPED MAGNESIUM ANODE ASSEMBLIES Filed July 30, 1965 INVENTOR- Char/9.5 E. Ale/son 96ENT United States Patent 3,390,016 PRIMARY CELL WITH PLURAL U-SHAPED MAGNESHUM ANODE ASSEMBLIES Charles E. Nelson, Midland, Mich., assignor to The Dow Chemical Company, Midland, l\ iich., a corporation of Delaware Filed July 30, 1965, Ser. No. 476,020 7 Claims. (Cl. 136100) ABSTRACT OF THE DISCLOSURE This invention relates to a fiat pack primary cell comprising, within a suitable generally enclosed casing having opposed ends, a plurality of anode assemblies of magnesium alloy, each of said anode assemblies being sheetlike in form and folded to form a two faced structure having a generally U-shaped transverse cross-sectional configuration, said anode assemblies being spaced apart in side-by-side relationship with a sheet of compressible material disposed between the inner faces thereof. An electrically insulating ionically conductive element is disposed between and covering adjacent outer faces of adjacent anode assemblies. At least one cathode electrode is disposed between and spaced from the adjacent outer faces of adjacent anode assemblies with cathode mix, being disposed between said adjacent outer faces of adjacent anode assemblies, the mix surrounding said cathode electrodes and separated from said outer faces by said ionically conductive elements.

The invention relates to improved ilat primary cells and especially to such cells which employ magnesium or magnesium alloy anodes.

For the purposes of the specification and claims, magnesium and magnesium base alloys containing at least 70 percent of magnesium are hereinafter referred to as magnesium metal.

'Dry cell batteries which employ magnesium as the anode metal are desirable because such dry cells having equivalent capacity to dry cells containing zinc provide a higher voltage potential, are lighter in weight and smaller in size.

Problems arise in constructing and operating magnesium anode type primary cells because of physical expansion within the cell during use as the anode decomposition product forms.

Economic problems exist also, because of the relative cost of production of magnesium anode type primary cells as compared to the cost of producing other primary cells.

Further, there is a continuing need for primary cells having improved current delivering capacity per unit of volume and weight of the cells or cell pack.

Accordingly, a principal object of this invention is to provide an improved primary cell.

A further object of this invention is to provide an improved primary cell utilizing a magnesium anode.

Yet another object of this invention is to provide an improved magnesium anode primary cell having large current delivering capacity in relation to its size.

An ancillary object of this invention is to provide an improved primary cell which has means therein for compensating for expansion within the cell assembly as anode decomposition product is formed.

The invention, as well as additional objects and advantages thereof, will best be understood when the following detailed description is read in connection with the accompanying drawing, in which:

FIG. 1 is an isometric view of a cell in accordance with this invention;

FIG. 2 is a sectional view taken along the line 2-2 of FIG. 1, and

FIG. 3 is a sectional view taken along the line 3-3 of FIG. 2.

Referring to the drawing, there is shown a primary cell, indicated generally by the numeral 10, enclosed in a suitable outer casing 12. A terminal, such as the terrninal 14, for example, is disposed at each end of the cell and is accessible, for example, through the aperture 16 in the casing 12.

Referring to FIGS. 2 and 3, as well as to FIG. 1, it may be seen that the cell 10 has a plurality of anodes 18, 20, 22. Each of the anodes is made of a substantially rectangular sheet of magnesium alloy bent to have a generally U-shaped transverse cross-sectional configuration and in which the folds of the anode are substantially parallel with each other.

A sheet 24, 26 or 2 3 of compressible material is disposed between the adjacent folds of each U-shaped anode, the sheets 24, 26 or 28 being substantially as thick as the spacing between the anode folds.

A separator sheet 56, 5'8 or 60 which is ionically conductive but electronically nonconductive is disposed against the facing surfaces of adjacent pairs of anodes.

Pairs of rod-like cathode electrodes 30, 32, 34 usually carbon rods, are disposed between the facing surfaces of adjacent pairs of anodes, e.g., the rods 30 being disposed between the facing surfaces of anodes 20 and 22.

The space between the cathode electrodes 34, 32, 30 and the separators 56, SS, 60, respectively is substantially filled with a suitable cathode mix which is tampcd into place.

The cathode terminal 14 is a metal plate-like element which is separated from the separator 46 by a sheet of fluid impervious electrically insulating material 62.

The cathode electrodes 30, 32, and 34 and the terminal 14 are electrically connected together by means of the leads 36, 33, 40. j

The anodes 18, 20, 22 are connected together at their base ends by leads 42, 44.

The face 54- of the anode 22, which may be contacted through the aperture 52 in the casing 12, serves as the positive electrode of the cell.

Although this cell is connected in parallel to provide a high output cell, cells in accordance with this invention may be connected in series or in parallel with other cells in any suitable manner.

Cells made in accordance with this invention are compact in relation to their current output capabilities, and will retain their configuration, because of the compressible material 24, 26, 28 without bulging as anode decomposition product is formed.

Further, although the usual means will be employed to prevent moisture loss from the cells during storage or use, moisture in the cathode mix may be replenished by malting the compressible sheets 24, 26 or 28 of an open pored material such as open pored expanded polystyrene, for example, which will store water and release it on compression as the anode decomposition product is formed.

In instances where the material 24, 2d, 2.0 is loaded with water, it is preferable that the surface of the anode adjacent to the water laden material have a corrosion inhibiting coating thereon on that the sides of the sheet 24, 26, 28 which are adjacent to the anodes be fluid impervious and thus release water into the cell only through their edges.

The magnesium metal anodes 18, 20, 22 may be formed of any suitable magnesium alloy, for example, the quick acting alloy containing aluminum and minor amounts of indium. Suitable alloys are described in US. patents 2,934,583 and 3,038,019.

The cushioning means or compressible material 24, 26, 28 is formed of any compressible non-conductive material which exhibits substantial compression strength, but is yieldingly compressible. While a pad formed of jute or sisal fibers or horsehair or shredded rubber or latex impregnated natural fibers may be used, it is preferred to use a material which exhibits a relatively high threshold resistance to compression, yet a relatively constant progression in resistance to compression, once threshold pressure is exceded, until the material has undergone a very substantial reduction in thickness, e.g., 75 to 90 percent reduction. Therefore, the ratio of total void space to volume occupied by solid matter in the material is preferably quite high, e.g., at least 4:1. Preferably the material exhibits a resilient resistance to compression such that it is not compressed more than one-third under a load of to 50 pounds per square inch.

The materials which appear to best exhibit the foregoing desired properties are the resilient expanded, or foamed, synthetic plastics, e.g., Pelaspan expanded polystyrene, or expanded plasticized polyvinyl chloride. Such expanded plastics are cellular, generally having closed or substantially closed cells. Brittle materials are generally to be avoided as they tend to compress irreversibly or to simply break down into particulate material. In general, those expanded plastics which will not break or crack when bent over a mandrel having a radius ten times the thickness of the layer are usable for batteries in normal or heavy service involving moderate to rough handling, or jarring.

Generally, a layer of compressible material at least one-sixteenth inch thick must be used with each anode assembly. A layer of about one-eighth to one-quarter inch thick for each anode assembly is suitable for most batteries. A layer thicker than about one-quarter inch may be used where space requirements permit, but the additional thickness is of no marked advantage.

The cathode mix 46, 48, 50 may be made up of any suitable composition normally employed for primary dry cells having magnesium anodes. Such mix cake is also known as a depolarizing mass. The mix cake is made up from a mixture of manganese dioxide and carbon black which is readily compressed or molded into cake form after being moistened with the electrolyte. A suitable mixture contains from 75 to 95 percent by weight manganese dioxide and the balance carbon black. A desirable mixture consists of 90 percent by weight MnO (gold coast ore) and 10 percent acetylene black.

The electrolyte is prepared by dissolving an alkali metal bromide, alkaline earth metal bromide or ammonium bromide in water in a concentnation between about grams per liter and that producing a nearly saturated solution at ordinary temperatures. The actual concentration used does not appear to be critical, although for best results certain concentrations are to be preferred depending upon the particular bromide or combination of bro mides used. For example, preferred concentrations of the alkali metal bromides are from about 150 to 500 grams of the salt per liter of solution. Of the alkali metal bromides, lithium bromide produces the most desirable results, particularly in concentrations of about 300 grams per liter. Similar concentrations may be used with the alkaline earth metal bromides, which include the bromides of magnesium, calcium, barium and strontium. Of these, magnesium bromide is to be preferred. Its most effective concentration is about 300 grams per liter of solution.

While a single bromide may be used as the electrolyte, better results are had with combinations of the aforesaid bromides, particularly combinations of an alkali metal bromide with an alkaline earth metal bromide, such better results being manifested in greater shelf life and higher capacity.

It is desirable to include in the electrolyte an alkali metal, alkaline earth metal or ammonium, salt of chromic acid in corrosion inhibiting amounts, such as from 0.01 gram per liter of solution to concentrations producing saturation in the presence of the bromide therein. A preferred concentration of the chromic acid salt is 0.05 to 2 grams per liter of solution. A number of specific suitable electrolyte compositions are set forth in U.S. Patents 2,547,907 and 2,547,908.

The porous separators 56, 58, 60 may be formed, for example, of a layer of blotterike material, such as a Kraft paper about 6 to 12 mills thick which is highly porous and of .a type normally used in such battery construction. A thicker layer of separator material may be used if desired. The porous separator is thoroughly wetted with electrolyte and serves to hold the electrolyte in place between the immediately adjacent metal anode and the mix cake.

What is claimed is:

1. A flat pack primary cell comprising, within a suitable generally enclosed casing having opposed ends, a plurality of anode assemblies of magnesium alloy, each of said anode assemblies being sheet-like in form and folded to form a two faced structure having a generally U-shaped transverse cross-sectional configuration, said anode assemblies being spaced apart in side-by-side relationship, each anode assembly having a sheet of compressible material disposed between the inner faces thereof, a plurality of electrically insulating ionically conductive elements, one of said ionically conductive elements being disposed between and covering adjacent outer faces of adjacent anode assemblies, a plurality of cathode electrodes, at least one of said cathode electrodes being disposed between and spaced from the adjacent outer faces of adjacent anode assemblies, cathode mix, said cathode mix being disposed between said adjacent outer faces of adjacent anode assemblies, surrounding said cathode electrodes and separated from said outer faces by said ionically conductive elements, means electrically connecting together each of said cathode elements, means electrically connecting together each of said anode assemblies, and terminal means, one terminal means being at each nd of said housing, one terminal means being a metal plate electrically connected to said cathode electrodes and the other terminal means being an outer face of an anode assembly.

2. A primary cell in accordance with claim 1, wherein said cathode electrodes are carbon rods.

3. A primary cell in accordance with claim 1, wherein said anode assembly faces are parallel with one another.

4. A primary cell in accordance with claim 1, wherein at least two of said cathode electrodes are disposed b tween adjacent faces of adjacent anode assemblies.

5. A primary cell in accordance with claim 1, wherein said compressible material is a cellular plastic material.

6. A primary cell in accordance with claim 1, wherein said compressible material is a moisture laden open celled material.

7. A primary cell in accordance with claim 6, wherein said open celled material is expanded polystyrene.

References Cited UNITED STATES PATENTS 522,127 6/1894 Timm l3687 2,859,265 11/1958 George 136100 FOREIGN PATENTS 759,584 10/ 1956 Great Britain.

ALLEN B. CURTIS, Primary Examiner.

WINSTON A. DOUGLAS, Examiner.

C. F. LEFEVOUR, Assistant Examiner. 

